So what are the chances of getting infected after vaccination? Nobody knows for sure.
Evidently, no vaccine is 100% effective in preventing infections.
During the Moderna trial, for instance, 11 patients out of the 15,210 who were vaccinated got infected.
Such infections however make up a small percentage of people who are fully vaccinated.
As tens of millions of people are vaccinated, more and more such cases will be reported.
“Vaccine efficacy may measure different aspects of disease like prevention of infection or preventing mild, moderate or severe disease. None of the approved COVID-19 vaccines has claimed to prevent infection and the 70-95% efficacy claimed by them is at preventing symptomatic disease,” says Prof V Anil Kumar, Clinical Professor & Head Microbiology, Amrita Institute of Medical Sciences Kochi, Kerala.
Preventing infection is not an achievable target for respiratory viral diseases like SARS-CoV-2. With mutations happening in the spike protein, newer variants are emerging which theoretically will show some degree of immune escape, thereby further reducing the effectiveness of the approved vaccines as was seen in the case of the South Africa variant B1.351.
Vaccines prevent illness, but maybe not an infection.
COVID-19 vaccines are being authorised based on how well they can keep one from getting sick, needing hospitalisation and dying. Some yet-to-be-peer-reviewed studies suggest that those that do develop symptomatic COVID-19 infection after vaccination have less severe outcomes.
In addition to the overall reduction in cases, early data suggest that any cases that do occur in older vaccinated people are around as half as likely to lead to hospitalisation and/or death.
A report brought out by Public Health England on 22 February 2021 on monitoring the early impact and effectiveness of COVID-19 vaccination in England found a higher level of protection (probably above 75%) against severe disease from a single dose of Pfizer vaccine in those over 80. This is supported by early data on protection against hospitalisation from Scotland.
For now, researchers are yet to figure out how effective vaccines are at preventing the coronavirus from infecting, or at keeping one from passing it on to others — which is crucial for preventing the emergence of newer variants and mutations.
According to Prof Anil Kumar, as long as any vaccine is able to prevent severe disease and hospitalisations it should be actively recommended. Having some form of anti-SARS-CoV-2 specific antibodies is better than having none.
Suffering a common cold with sore throat and fever, which subsides after two to three days of symptomatic treatment, is part of normal life and cannot be eradicated by any vaccine. Seasonal flu used to kill many before COVID-19 and will continue to kill after COVID-19 irrespective of the number of vaccines that are introduced.
The best example is H1N1 which can cause everything that SARS-CoV-2 can and has a potent vaccine which is readily available but is not taken even by healthcare workers. Humans are known to take risks and vaccination is an acceptable risk that everyone should take, he remarks.
For now, it looks likely that the SARS-CoV-2 is likely to end up like the influenza virus where a new vaccine is introduced every season based on the predominant variant circulating in that region.
The concept of a booster dose with a vaccine containing the variant strain is already being considered. “I wouldn’t be surprised if a polyvalent vaccine containing different strains is introduced in the near future,” avers Prof Anil Kumar.
Since vaccinated individuals can get an asymptomatic infection and also transmit it to susceptible individuals, emphasis on non-pharmacological measures should continue till 60-70% of the population gets vaccinated, say the experts.