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Side Effects of COVID-19 Vaccines

 
COVID-19 vaccines are safe, and getting vaccinated will help protect you against developing severe COVID-19
disease and dying from COVID-19. You may experience some mild side effects after getting vaccinated, which
are signs that your body is building protection.
Why it’s normal to have mild side effects from vaccines
Vaccines are designed to give you immunity without the dangers of getting the disease. It’s common to
experience some mild-to-moderate side effects when receiving vaccinations. This is because your immune
system is instructing your body to react in certain ways: it increases blood flow so more immune cells can
circulate, and it raises your body temperature in order to kill the virus.
Mild-to-moderate side effects, like a low-grade fever or muscle aches, are normal and not a cause for alarm:
they are signs that the body’s immune system is responding to the vaccine, specifically the antigen (a
substance that triggers an immune response), and is gearing up to fight the virus. These side effects usually go
away on their own after a few days.
Common and mild or moderate side effects are a good thing: they show us that the vaccine is working.
Experiencing no side effects doesn’t mean the vaccine is ineffective. It means everybody responds differently. 
Common side effects of COVID-19 vaccines
Like any vaccine, COVID-19 vaccines can cause side effects, most of which are mild or moderate and go away
within a few days on their own. As shown in the results of clinical trials, more serious or long-lasting side
effects are possible. Vaccines are continually monitored to detect adverse events.
Reported side effects of COVID-19 vaccines have mostly been mild to moderate and have lasted no longer
thana few days. Typical side effects include pain at the injection site, fever, fatigue, headache, muscle pain,
chills and diarrhoea. The chances of any of these side effects occurring after vaccination differ according to the
specific vaccine.
COVID-19 vaccines protect against the SARS-CoV-2 virus only, so it’s still important to keep yourself healthy
and well.
Less common side effects
Upon receiving the vaccine, a person should be requested to stay for 15–30 minutes at the vaccination site so
health workers are available in case of any immediate reactions. Individuals should alert their local health
providers following vaccination if they experience any unexpected side effects or other health events – such as
side effects lasting more than three days. Less common side effects reported for some COVID-19 vaccines
have included severe allergic reactions such as anaphylaxis; however, this reaction is extremely rare. 
National authorities and international bodies, including WHO, are closely monitoring for any unexpected side
effects following COVID-19 vaccine use.
Long-term side effects
Side effects usually occur within the first few days of getting a vaccine. Since the first mass vaccination
programme started in early December 2020, hundreds of millions of vaccine doses have been administered.
There have been concerns about COVID-19 vaccines making people sick with COVID-19. But none of the
approved vaccines contain the live virus that causes COVID-19, which means that COVID-19 vaccines cannot
make you sick with COVID-19.
After vaccination, it usually takes a few weeks for the body to build immunity against SARS-CoV-2, the virus
that causes COVID-19. So it’s possible a person could be infected with SARS-CoV-2 just before or after
vaccination and still get sick with COVID-19. This is because the vaccine has not yet had enough time to
provide protection.
Experiencing side effects after getting vaccinated means the vaccine is working and your immune system is
responding as it should. Vaccines are safe, and getting vaccinated will help protect you against COVID-19.+
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Vaccinations and the impact of COVID-19 – our continuously-updated data for Israel

Israel has conducted the fastest campaign to vaccinate its population against COVID-19 so far. The world is
now watching how the pandemic in the country evolves to assess whether vaccinations are having the
intended effect, and how effective they might be in preventing infection, severe disease and death.

To answer the question of how the vaccination campaign impacts the evolution of COVID-19 requires a
thorough analysis based on an epidemiological model. All we can do here is to present some relevant data to
track what is happening. Note that the changes in case rates, hospitalizations and deaths cannot be solely
attributed to the impact of vaccination.

To be able to track the development of the pandemic in Israel, we show the data on vaccinations, confirmed
cases, hospitalizations, ICU admissions, and deaths in the following charts. The data presented below comes
from multiple sources:

 Data on vaccinations, confirmed cases, and hospitalizations by age and by geographical group (early or
late vaccination) comes from the work of Hagai Rossman, Smadar Shilo, Tomer Meir, Malka Gorfine, Uri
Shalit, and Eran Segal.1 Their preprint paper can be found here. This data will be updated every few days.
 Data on total vaccinations (from our global dataset on vaccinations) and confirmed cases and deaths
(from Johns Hopkins University) is updated daily.
 Data on confirmed cases by age group, and on hospitalizations and ICU admissions, comes from the
Israeli government and is updated weekly.
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The effects of virus variants on COVID-19 vaccines

All viruses – including SARS-CoV-2, the virus that causes COVID-19 – evolve over time. When a virus
replicates or makes copies of itself, it sometimes changes a little bit, which is normal for a virus. These
changes are called “mutations”. A virus with one or more new mutations is referred to as a “variant” of the
original virus.

What causes a virus to change to a new variant?

When a virus is widely circulating in a population and causing many infections, the likelihood of the virus
mutating increases. The more opportunities a virus has to spread, the more it replicates – and the more
opportunities it has to undergo changes.

Most viral mutations have little to no impact on the virus’s ability to cause infections and disease. But
depending on where the changes are located in the virus’s genetic material, they may affect a virus’s
properties, such as transmission (for example, it may spread more or less easily) or severity (for example, it
may cause more or less severe disease). 

What impact do the new variants of the COVID-19 virus have on vaccines?

The COVID-19 vaccines that are currently in development or have been approved are expected to provide at
least some protection against new virus variants because these vaccines elicit a broad immune response
involving a range of antibodies and cells. Therefore, changes or mutations in the virus should not make
vaccines completely ineffective. In the event that any of these vaccines prove to be less effective against one
or more variants, it will be possible to change the composition of the vaccines to protect against these variants.

Data continues to be collected and analysed on new variants of the COVID-19 virus. WHO is working with
researchers, health officials and scientists to understand how these variants affect the virus’s behaviour,
including their impact on the effectiveness of vaccines, if any. See WHO’s Disease Outbreak News to get up-
to-date information on the impact of COVID-19 virus variants on the effectiveness of the different vaccines.
This is an area where the evidence remains preliminary and is developing quickly. 

While we are learning more, we need to do everything possible to stop the spread of the virus in order to
prevent mutations that may reduce the efficacy of existing vaccines. In addition, manufacturers and the
programmes using the vaccines may have to adjust to the evolution of the COVID-19 virus: for example,
vaccines may need to incorporate more than one strain when in development, booster shots may be required,
and other vaccine changes may be needed. Trials must also be designed and maintained to allow any
changes in efficacy to be assessed, and must be of sufficient scale and diversity to enable clear interpretation
of results. Studies of the impact of vaccines as they are deployed are also essential in order to understand
their impact.

What is WHO doing to monitor and understand the impact of virus variants on the efficacy of COVID-19

vaccines?

 
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WHO has been tracking mutations and variants since the start of the COVID-19 outbreak. Our global SARS-
CoV-2 laboratory network includes a dedicated Virus Evolution Working Group, which aims to detect new
changes quickly and assess their possible impact.

Research groups have carried out genomic sequencing of the COVID-19 virus and shared these sequences on
public databases, including GISAID. This global collaboration allows scientists to better track how the virus is
changing. WHO recommends that all countries increase the sequencing of the COVID-19 virus where possible
and share data to help one another monitor and respond to the evolving pandemic.

WHO has also established a SARS-CoV-2 Risk Monitoring and Evaluation Framework to identify, monitor and
assess variants of concern. It will involve components like surveillance, research on variants of concern, and
evaluation of the impact on diagnostics, therapeutics and vaccines. The framework will serve as a guide for
manufacturers and countries on changes that may be needed for COVID-19 vaccines.

How can we prevent future new variants of the COVID-19 virus?

Stopping the spread at the source remains key. Current measures to reduce transmission – including frequent
hand washing, wearing a mask, physical distancing, good ventilation and avoiding crowded places or closed
settings – continue to work against new variants by reducing the amount of viral transmission and therefore
also reducing opportunities for the virus to mutate.

Scaling up vaccine manufacturing and rolling out vaccines as quickly and widely as possible will also be critical
ways of protecting people before they are exposed to the virus and the risk of new variants. Priority should be
given to vaccinating high-risk groups everywhere to maximize global protection against new variants and
minimize the risk of transmission. Moreover, ensuring equitable access to COVID-19 vaccines is more critical
than ever to address the evolving pandemic. As more people get vaccinated, we expect virus circulation to
decrease, which will then lead to fewer mutations.

Why is it important to get vaccinated even if there are new variants of the virus?

Vaccines are a critical tool in the battle against COVID-19, and there are clear public health and lifesaving
benefits to using the tools we already have. We must not put off getting vaccinated because of our concerns
about new variants, and we must proceed with vaccination even if the vaccines may be somewhat less
effective against some of the COVID-19 virus variants. We need to use the tools we have in hand even while
we continue to improve those tools. We are all safe only if everyone is safe.

Effect of vaccination on transmission of COVID-

19: an observational study in healthcare workers
and their households
 View ORCID ProfileAnoop S V
Shah, Ciara Gribben, Jennifer Bishop, Peter Hanlon, David Caldwell, Rachael Wood, Martin Reid, Ji
m McMenamin, David Goldberg, Diane Stockton, Sharon Hutchinson, Chris Robertson, Paul
M McKeigue, Helen M Colhoun, David A McAllister
doi: https://doi.org/10.1101/2021.03.11.21253275
This article is a preprint and has not been peer-reviewed [what does this mean?]. It reports
new medical research that has yet to be evaluated and so should not be used to guide clinical
practice.
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Abstract
Background The effect of vaccination for COVID-19 on onward transmission is unknown.
Methods A national record linkage study determined documented COVID-19 cases and hospitalisations
in unvaccinated household members of vaccinated and unvaccinated healthcare workers from
8th December 2020 to 3rd March 2021. The primary endpoint was COVID-19 14 days following the first
dose.
Results The cohort comprised of 194,362 household members (mean age 31·1 ± 20·9 years) and
144,525 healthcare workers (mean age 44·4 ± 11·4 years). 113,253 (78·3%) of healthcare workers
received at least one dose of the BNT162b2 mRNA or ChAdOx1 nCoV-19 vaccine and 36,227 (25·1%)
received a second dose. There were 3,123 and 4,343 documented COVID-19 cases and 175 and 177
COVID-19 hospitalisations in household members of healthcare workers and healthcare workers
respectively. Household members of vaccinated healthcare workers had a lower risk of COVID-19 case
compared to household members of unvaccinated healthcare worker (rate per 100 person-years
9·40 versus 5·93; HR 0·70, 95% confidence interval [CI] 0·63 to 0·78). The effect size for COVID-19
hospitalisation was similar, with the confidence interval crossing the null (HR 0·77 [95% CI 0·53 to 1·10]).
The rate per 100 person years was lower in vaccinated compared to unvaccinated healthcare workers for
documented (20·13 versus 8·51; HR 0·45 [95% CI 0·42 to 0·49]) and hospitalized COVID-19 (0·97 versus
0·14; HR 0·16 [95% CI 0·09 to 0·27]). Compared to the period before the first dose, the risk of
documented COVID-19 case was lower at ≥ 14 days after the second dose for household members (HR
0·46 [95% CI 0·30to 0·70]) and healthcare workers (HR 0·08 [95% CI 0·04 to 0·17]).
Interpretation Vaccination of health care workers was associated with a substantial reduction in COVID-
19 cases in household contacts consistent with an effect of vaccination on transmission.

Competing Interest Statement

PM and HC have received research grants from AstraZeneca. There are no other competing
interests.

Clinical Protocols

http://www.encepp.eu/encepp/viewResource.htm?id=39737
https://github.com/dmcalli2/hcw_vax

Funding Statement

ASVS is funded via the British Heart Foundation through an intermediate clinical research fellowship
(FS/19/17/34172), and DAM is funded via a Wellcome Trust intermediate clinical fellowship and Beit
fellowship (201492/Z/16/Z). The funders had no role in the study design; in the collection, analysis,
and interpretation of data; in the writing of the report; and in the decision to submit the article for
publication.

Author Declarations

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics
committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described
are given below:

This project was approved by the NHS Public Benefit and Privacy Panel (2021-0013) for use of the
data and linkage.

All necessary patient/participant consent has been obtained and the appropriate institutional forms
have been archived.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered
with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in
the manuscript has been registered and the trial registration ID is provided (note: if posting a
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prospective study registered retrospectively, please provide a statement in the trial ID field explaining
why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR
Network research reporting checklist(s) and other pertinent material as supplementary files, if
applicable.

Yes

Paper in collection COVID-19 SARS-CoV-2 preprints from medRxiv and bioRxiv