These are extracts from a more readable article from the scientist but even if you google and read research papers you will find lots of studies that point to less than 99.9 agreement. Like I said it's complex.
Vaccinating as many people as possible with initial doses before moving on to second doses is intended as the fastest means of inducing a good level of protection within the population. But some experts say they worry that this constitutes a giant experiment in viral evolution, where the potential consequences remain troublingly unclear.
Among those concerned is Paul Bieniasz, a virologist at the Rockefeller University. “Rolling out a partially effective vaccine regime in the peak of a highly prevalent viral epidemic is just not a great idea if one of your goals is to avoid vaccine resistance,” he says.
There’s a chance, Bieniasz explains, that people waiting for their second dose may have a sub-optimal level of immunity that places selective pressure on the virus. If someone were to become infected during the interval between jabs, that pressure could allow for the emergence of a mutant version of SARS-CoV-2 able to shake off a person’s immune response—a so-called escape variant. Any such variant that also proved capable of causing severe disease could potentially spark a whole new, devastating wave of infections and deaths.
Anthony Fauci, President Joe Biden’s chief medical adviser on COVID-19, said last month at a virtual World Economic Forum panel that delaying the second dose of a COVID-19 vaccine could increase the likelihood of an escape variant emerging. “It may not be the case, but it gets risky,” he told the audience.
Scientists advising the UK government have considered the same scenario.
In a paper published last month, they wrote, “in the short-term, delaying the second dose would be expected to somewhat increase the probability of emergence of vaccine resistance.” But quantifying the risk is nigh on impossible.
We can’t really put a number on it,” says Björn Meyer, a virologist at the Pasteur Institute in Paris, referring to the risk of delayed dosing leading to the evolution of an escape variant. Every time the virus replicates there is a chance that it could mutate into a more transmissible or more deadly form. In a single individual, the odds of this happening are vanishingly small but the picture changes somewhat when you consider that tens of millions of people are currently waiting for their second dose, notes Meyer.