Experts are saying transmission of the novel coronavirus is still possible as scientists do not know how long vaccine-induced immunity will last or transmission can occur within the window between doses.

Despite the manufacturers of the COVID vaccine recommending a delay of no more than three weeks between the two required doses, the UK and some surrounding countries have decided to extend the window between the required two shots.

Amidst criticism from healthcare experts and scientist, the UK in December agreed to delay second shots by 12 weeks. This was a calculated risk to allegedly allow time for as many people as possible to receive their first shot of the Pfizer-BioNTech or Oxford-AstraZeneca vaccine – the two being used in the UK.

These criticisms bothered on there being no adequate study that that determines how long protection from just one shot would last.

However, data published by Public Health England which focused on the elderly (who are considered the frailest and least likely to mount a strong immune response) showed that a single shot of either the Oxford-AstraZeneca or the Pfizer-BioNTech jab reduces the chance of needing hospital treatment by more than 80 percent. 

This outcome might convince people that their first shot might provide adequate immunity but experts are saying the second dose is still important for boosting immunity, reducing hospitalization risk even further and for the length of time for which you are protected. Furthermore, while there is increasing evidence of the vaccines reducing transmission, more research is needed.

For instance, the Johnson & Johnson vaccine which was designed to provide adequate immunity with on shot vaccine was tested in a trial involving nearly 44,000 participants in the United States, Latin America and South Africa. In the US cohort, it was shown to be 72-percent effective. However, it was shown to be less effective against the newer South African and Brazilian strains of the virus – giving protection against the virus in only 55 percent and 67 percent of participants respectively.

Results from the first two US-authorised vaccines, Pfizer-BioNtech and Moderna, were considerably stronger, reducing symptomatic infection by about 95 percent. But those vaccines require two doses to achieve that level of immunity.

While experts are still working hard to understand how long vaccine-induced immunity will last, people are advised to still maintain safety rules like mask-wearing and social distancing until after the second dose of the vaccine has been taken.